''Ixodes scapularis'' is commonly known as the deer tick or black-legged tick (although some people reserve the latter term for ''

Ixodes pacificus ''Ixodes pacificus'', the western black-legged tick, is a species of parasitic tick found on the western coast of North America. ''I. pacificus'' is a member of the ''Ixodidae'' (hard-bodied) family. It is the principal vector of Lyme disease in ...

'', which is found on the west coast of the US), and in some parts of the US as the bear tick. It was also named ''Ixodes dammini'' until it was shown to be the same species in 1993. It is a hard-bodied

tick Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by ...

found in the eastern and northern Midwest of the United States as well as in southeastern Canada. It is a

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

for several diseases of animals, including humans (

Lyme disease Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by the ''Borrelia'' bacterium, which is spread by ticks in the genus ''Ixodes''. The most common sign of infection is an expanding red rash, known as erythema migran ...

babesiosis Babesiosis or piroplasmosis is a malaria-like parasitic disease caused by infection with a eukaryotic parasite in the order Piroplasmida, typically a ''Babesia'' or '' Theileria'', in the phylum Apicomplexa. Human babesiosis transmission via ...

anaplasmosis Anaplasmosis is a tick-borne disease affecting ruminants, dogs, and horses, and is caused by ''Anaplasma'' bacteria. Anaplasmosis is an infectious but not contagious disease. Anaplasmosis can be transmitted through mechanical and biological vector ...

, Powassan virus disease, etc.) and is known as the deer tick owing to its habit of

parasitizing Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...

the

white-tailed deer The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...

. It is also known to parasitize mice, lizards, migratory birds, etc. especially while the tick is in the larval or nymphal stage.

Description

The image shown here—and in fact, most images of ''Ixodes scapularis'' that are commonly available—show an adult female that is unengorged, that is, an adult female that has not had a blood meal. This is natural, since ticks are generally removed immediately upon discovery to minimize the chance of disease. However, the abdomen that holds blood is much larger when engorged; therefore, an engorged specimen of ''I. scapularis'' (see photo below) could easily be mistaken for an entirely different tick. When the deer tick has consumed a blood meal, its abdomen is a light grayish-blue color. The tick itself is naturally black when unfed. In identifying an engorged tick, concentrating on the legs and upper part of the body is helpful.

Behavior

''Ixodes scapularis'' has a 2-year lifecycle, during which time it passes through three stages: larva, nymph, and adult. The tick must take a blood meal at each stage before maturing to the next. Deer tick females latch onto a host and drink its blood for 4–5 days. Deer are the preferred host of the adult deer tick, but it is also known to feed on small rodents. After she is engorged, the tick drops off and

overwinters Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activ ...

in the leaf litter of the forest floor. The following spring, the female lays several hundred to a few thousand eggs in clusters. Transtadial (between tick stages) passage of ''

Borrelia burgdorferi ''Borrelia burgdorferi'' is a bacterial species of the spirochete class in the genus '' Borrelia'', and is one of the causative agents of Lyme disease in humans. Along with a few similar genospecies, some of which also cause Lyme disease, it mak ...

'' is common. Vertical passage (from mother to egg) of ''Borrelia'' is uncommon. Like other ticks, ''I. scapularis'' is hardy. It can be active after a hard

frost Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a gas) ...

, as daytime temperatures can warm it enough to keep it actively searching for a host. In the spring, it can be one of the first

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s to become active. Deer ticks can be quite numerous and seemingly

gregarious Sociality is the degree to which individuals in an animal population tend to associate in social groups (gregariousness) and form cooperative societies. Sociality is a survival response to evolutionary pressures. For example, when a mother wasp ...

As disease vector

''Ixodes scapularis'' is the main

in North America. The CDC reported over 30,000 new cases of the disease in 2016 alone, the majority of which were contracted in the summer months, which is when ticks are most likely to bite humans. While adult deer ticks are more likely to carry and transmit ''Borrelia burgdorferi'', it is more common for the hard-to-spot nymphal stage to infect humans. It can also transmit other ''Borrelia'' species, including ''

Borrelia miyamotoi ''Borrelia miyamotoi'' is a bacterium of the spirochete phylum in the genus '' Borrelia''. A zoonotic organism, ''B. miyamotoi'' can infect humans through the bite of several species of hard-shell ''Ixodes'' ticks, the same kind of ticks that sp ...

''. Ticks that transmit '' B. burgdorferi'' to humans can also carry and transmit several other parasites, such as ''

Babesia microti Babesia microti is a parasitic blood-borne piroplasm transmitted by deer ticks. ''B. microti'' is responsible for the disease babesiosis, a malaria-like disease which also causes fever and hemolysis. Life cycle The life cycle of ''B. microti ...

'' and ''

Anaplasma phagocytophilum ''Anaplasma phagocytophilum'' (formerly ''Ehrlichia phagocytophilum'') is a Gram-negative bacterium that is unusual in its tropism to neutrophils. It causes anaplasmosis in sheep and cattle, also known as tick-borne fever and pasture fever, and ...

'', which cause the diseases

and

human granulocytic anaplasmosis Human granulocytic anaplasmosis (HGA) is a tick-borne, infectious disease caused by ''Anaplasma phagocytophilum'', an obligate intracellular bacterium that is typically transmitted to humans by ticks of the '' Ixodes ricinus'' species complex, i ...

(HGA), respectively. Among early Lyme disease patients, depending on their location, 2%–12% will also have HGA and 2%–40% will have babesiosis. Co-infections complicate Lyme symptoms, especially diagnosis and treatment. It is possible for a tick to carry and transmit one of the co-infections and not ''Borrelia'', making diagnosis difficult and often elusive. The

Centers for Disease Control The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...

's emerging infectious diseases department did a study in rural New Jersey of 100 ticks, and found 55% of the ticks were infected with at least one of the pathogens. Deer, the preferred mammalian hosts of adult ''I. scapularis'', cannot transmit ''Borrelia''

spirochaete A spirochaete () or spirochete is a member of the phylum Spirochaetota (), (synonym Spirochaetes) which contains distinctive diderm (double-membrane) gram-negative bacteria, most of which have long, helically coiled (corkscrew-shaped or s ...

s to ticks. Ticks acquire Lyme disease microbes by feeding on infected

mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...

and other small rodents as nymphs or larvae. One of the keys of the success of ''I. scapularis'' as a ''Borrelia'' vector relies on its ability to limit the proliferation of the spirochaete. This is due to the activity of domesticated amidase effector (dae) genes. Dae genes are a family of horizontally acquired genes related to type VI secretion amidase effector (tae) genes in certain bacteria which encode toxins honed to mediate interbacterial antagonism. Once transferred to eukaryotes tae genes confer novel antibacterial capabilities; this provides a selective advantage to the tick and to other eukaryotes also: tae genes have been transferred from bacteria to eukaryotes at least in six independent events. In particular, ''I. scapularis'' have inherited the dae 2 family from a common ancestor between ticks and mites. The product of dae2 expression has been shown to degrade bacterial peptidoglycan of different species and particularly from ''B. burgdorferi'', but does not limit initial acquisition of the bacterium by the tick. Dae2 contributes to the innate ability of ''I. scapularis'' to control '' B. burgdorferi'' levels after its acquisition. This has potential ramifications for Lyme disease transmission, as spirochaete load in the tick can influence transmission efficiency. A recent study has identified the alpha-gal sugar in the tick, and they have suggested that it may also be involved in the onset of red meat allergy ( Alpha-Gal Syndrome or Mammalian Meat Allergy, MMA).

Genome sequencing

The genome of ''I. scapularis'' has been sequenced.''Ixodes scapularis'' genome sequence at VectorBase
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References

External links